EMERSON LC320EM3F WON'T START: SOLVED

:taps2:

This is a LCD TV brand EMERSON, model LC320EM3F and is completely death.

At first revision, we detected some bad components in the switching power source:

Switching MOSFET K10A50D, RESISTOR 0.19 Ohm, 2W, transistor switching controler 2SC5344, Zener Diode 1ZB36 (36V) and the 4A fuse.

I had the SM of LC320EM9 model, so, the values of the components are different.

I replace them all twice and they always broke again! FRUSTRATING!

Then I realyze that changin the values nearly to the LC320EM9 model, I would obtain better results (see FILE ATTACHED)

I replace the 0.19Ohm resistor by a 0.39Ohm, maximizing the pulse received for the control transistor, for that purpose, also changed the 2.4KOhm resistor for 5.6KOhm. The switching MOSFET used was IRF640 replacing K10A50D, and transistor 2SC5344 was replaced by 2N5551. Finally we add a Zener diode not included in original board (marked with blue circle) limiting the colector voltage and gate voltage to 26V.

For short, when we connect the power cord, every thing was fine, except than voltages at secondary of main transformer, was only 3.2V DC in all rectifiers.

Found a diode in short-circuit (circled in red), replaced it and BINGO!, the TV return to live again!!!!

I Hope it serves as a nice experience for the future.